1. Fields of the Invention
The present invention relates to a method for manufacturing a conductive adhesive, especially to a method for manufacturing a conductive adhesive containing a one-dimensional (1D) conductive nanomaterial.
2. Descriptions of Related Art
One-dimensional (1D) nanostructures have low-dimensional physical and electronic transport properties and have been regarded as the most promising materials with features different from those of bulk materials due to its special structure in the last 10 years. One-dimensional (1D) nanostructures include nanowires, nanotubes, nanorods, nanopillars, nanofibrils, and quantum wires. 1D nanostructure is applied to nanoelectronic devices and functional components such as ultra-thin and full-color LED, printing equipment, field emission display (FED), low energy consumption nanowire LED, ammonia (NH3) sensors, hydrogen (H2) sensors, etc.
Nano-metal materials such as gold, tin, silver, platinum etc. have good electrical conductivity so that they are applied to interconnect materials. 1D metal nanomaterials are with unusual properties in the fields of optics, electricity, magnetism and chemistry. 1D metal nanomaterials have connected zero-dimensional metal nanomaterials in series so that 1D metal nanomaterials are with better electrical conductivity compared with zero-dimensional metal nanomaterials. Due to two kinds of dimensions of the nanomaterials, 1D metal nanomaterials still keep their unique nanoscale properties such as high activity, low sintering temperature, tunnelling effect etc. Thus 1D metal nanomaterials have broad applications such as Ultra Large Scale Integration (ULSIC) and optical conductive fiber. Metal nanowires that match with nanodots are used for connecting electronic parts so as to achieve high density arrangement in nanoscale electronics. Magnetic metal nanowires with good vertical magnetization are used as high density vertical magnetic recording materials. Quantum magnetic disks produced by template synthesis are used as nanoelectrode ensembles, applied to trace detection and gas sensors in the field of electrochemistry analysis.
Silver is the best conductive metal and is applied to coating material such as conductive silver paste with features of high electrical conductivity, stretchability, salt mist corrosion durability, and wide applicable temperature range. For further applications in electrical conductivity after nanolization, 1D silver nanowire is synthesized. 1D wire-like nanostructure has features of a good conductivity and lower temperature sintering. It is applied to electrodes, low temperature sintered conductive adhesives, superconductive thick film circuit, microwave absorbing materials, and electromagnetic wave absorbing materials and the amount of silver used is dramatically reduced.
As to the one dimensional conductive nanomaterials, carbon nanotube is the only commercial product available on the market now. For higher conductivity, metal materials such as silver or copper should be used. However, the mass production of silver or copper nanowires has not matured yet and the product is quite expensive. Thus there is a need to develop related techniques and metal materials are a new generation of materials.
1D silver nanostructures are mainly applied to electrical conductivity and biochemistry fields. For electrical conductivity, 1D silver nanostructures are prepared to form a transparent conductive film for electrode connection of semiconductors, solar cells and light emitting diode (LED) or are used in conductive coating for micro-electronic components and displays.
The applications of 1D silver nanostructures in biochemistry mainly includes biological microsensors and self-assembled DNA sensors. 1D conductive nanomaterial applied to transparent conductive films is mainly produced by precision etching. Catalyst is implanted by vapor deposition and then 1D silver nanostructures can grow into a network microstructure. Or 1D silver nanostructures are synthesis firstly by electrochemical etching template growth or wet chemical synthesis and then is arranged again. Yet the ways of arrangement are quite complicated. For example, the 1D silver nanostructures are produced by filtering, deposition and drying and then to form a film by micro-transfer printing technology. Or the film is produced by microscope probes or high temperature sintering. These ways are not proper for mass production and there are many restrictions on the substrate. The manufacturing cost is quite high. These are all opposite to the industrial mainstream-coating processes.
After being mixed with resin, nano silver can be coated directly and cured at low temperature. Refer to two related techniques, Chinese Patent. App. No. 10154638, silver nanowires are prepared by wet chemical synthesis. After purification and drying, the silver nanowires are mixed with epoxy resin or phenolic resin to be coated and a film is formed. As to Chinese Patent. App. No. 10050523, a conductive adhesive is formed by silver nanowires and acrylic resin. Then the conductive adhesive is coated. Although the above two patents report good conductivity of the conductive adhesive and the conductive film, the incompatibility between aqueous solution containing silver nanowires and solvent-based resin has not been discussed. Aggregation occurs while mixing nanomaterials with different surface properties and poor-dispersed conductive medium is unable to connect and form an electric circuit. Thus the dispersion is a main bottleneck in the technology of enhancing conductivity of nanomaterials, especially the silver nanowires with good conductivity. The present invention provides a method for manufacturing a conductive adhesive containing one-dimensional conductive nanomaterials. The conductive adhesives obtained according to the present invention have good conductivity. Moreover, the amount of conductive material used is dramatically reduced and the manufacturing processes are simplified.